In general, X-Y monitor scopes using a CRT as a display device include two sets of coordinates, i.e. "effective" display coordinates determined by the CRT per se, characteristics of the circuits associated therewith including an effect caused by the earth magnetism, and scale coordinates defined by a scale directly or separately provided on the screen of the CRT. When such a monitor is used, calibration is necessary in order to first check whether the sets of coordinates coincide with each other. In the calibration, a sine wave is conventionally applied to either the X axis (horizontal axis) input or Y axis (vertical axis) input of the monitor to cause a single linear locus to be displayed on the screen of the CRT so that the locus can be visually compared with the X or Y axis line of the scale coordinates, with which the locus should be aligned. If they deviate from each other, variable parameters of the display characteristics of the CRT scope, that is, the horizontal and vertical positions, horizontal and vertical gains and rotation are adjusted accordingly.
In such a conventional calibration method employing a single calibrating linear locus, since the parameters are adjusted mainly on the basis of either ends of the calibrating locus and the portion considered to be its midpoint, if the calibration is to be conducted more accurately, the number of fine adjustments required would increase thus resulting in a greater amount of time being required for the calibrating operation.
In addition, in stereo X-Y audio monitors, some monitors have, as scale coordinates, orthogonal R and L axes representing the levels of R and L channel signals, respectively, and some other monitors have orthogonal L-R and L+R axes representing a difference (L-R) and a sum (L+R), respectively, of the R-ch and L-ch signals. In the latter case, when either the horizontal L-R axis line or the vertical L+R axis line, which intersect at right angles with each other, is to be calibrated, a difference between the gains of the R channel (horizontal) and L channel (vertical) is extremely difficult to be discriminated from rotation caused by the earth magnetism, thus necessitating the expenditure of further time being taken in the calibration.
Accordingly, an object of the present invention is to provide a method and apparatus for calibrating a display which allows the calibrating operation to be simplified.
Another object of the present invention is to provide an apparatus for producing loci suitable for use in such a calibration.